Armchair astronomers find planet in quadruple star system

A family portrait of the PH1 planetary system: The newly discovered planet is depicted in this artist’s rendition transiting the larger of the two eclipsing stars it orbits. Off in the distance, well beyond the planet orbit, resides a second pair of stars bound to the planetary system. Credit: Haven Giguere/Yale

(Phys.org)—A joint effort of citizen scientists and professional astronomers has led to the first reported case of a planet orbiting twin suns that in turn is orbited by a second distant pair of stars.

Aided by volunteers using the Planethunters.org website, a Yale-led international team of astronomers identified and confirmed discovery of the phenomenon, called a circumbinary planet in a four-star system.

Only six planets are known to orbit two stars, according to researchers, and none of these are orbited by distant stellar companions.

"Circumbinary planets are the extremes of planet formation," said Meg Schwamb of Yale, lead author of a paper about the system presented Oct. 15 at the annual meeting of the Division for Planetary Sciences of the American Astronomical Society in Reno, Nevada. "The discovery of these systems is forcing us to go back to the drawing board to understand how such planets can assemble and evolve in these dynamically challenging environments."

Dubbed PH1, the planet was first identified by citizen scientists participating in Planet Hunters, a Yale-led program that enlists members of the public to review astronomical data from NASA's Kepler spacecraft for signs of planets. It is the project's first confirmed planet discovery.

A family portrait of the PH1 planetary system: The newly discovered planet is depicted in this artist's rendition transiting the larger of the two eclipsing stars it orbits. Off in the distance, well beyond the planet orbit, resides a second pair of stars bound to the planetary system. Credit: Haven Giguere/Yale.

The volunteers—Kian Jek of San Francisco and Robert Gagliano of Cottonwood, Arizona—spotted faint dips in light caused by the planet as it passed in front of its parent stars, a common method of finding extrasolar planets. Schwamb, a Yale postdoctoral researcher, led the team of professional astronomers that confirmed the discovery and characterized the planet, following observations from the Keck telescopes on Mauna Kea, Hawaii. PH1 is a gas giant with a radius about 6.2 times that of Earth, making it a bit bigger than Neptune.

"Planet Hunters is a symbiotic project, pairing the discovery power of the people with follow-up by a team of astronomers," said Debra Fischer, a professor of astronomy at Yale and planet expert who helped launch Planet Hunters in 2010. "This unique system might have been entirely missed if not for the sharp eyes of the public."

PH1 orbits outside the 20-day orbit of a pair of eclipsing stars that are 1.5 and 0.41 times the mass of the Sun. It revolves around its host stars roughly every 138 days. Beyond the planet's orbit at about 1000 AU (roughly 1000 times the distance between Earth and the Sun) is a second pair of stars orbiting the planetary system.

"The thousands of people who are involved with Planet Hunters are performing a valuable service," said coauthor Jerome Orosz, who earned his Ph.D. at Yale in 1996 and is now associate professor of astronomy at San Diego State University. "Many of the automated techniques used to find interesting features in the Kepler data don't always work as efficiently as we would like. The hard work of the Planet Hunters helps ensure that important discoveries are not falling through the cracks."

Gagliano, one of the two citizen scientists involved in the discovery, said he was "absolutely ecstatic to spot a small dip in the eclipsing binary star's light curve from the Kepler telescope, the signature of a potential new circumbinary planet."

He continued, "It's a great honor to be a Planet Hunter, citizen scientist, and to work hand-in-hand with professional astronomers, making a real contribution to science."

Jek expressed wonder at the possibility of the discovery: "It still continues to astonish me how we can detect, let alone glean so much information about another planet thousands of light years away just by studying the light from its parent star."

The paper is available on the arXiv preprint server and has been submitted to Astrophysical Journal. A team from Johns Hopkins University has been working on a separate paper on aspects of the planetary system.

AbstractWe report the discovery and confirmation of a transiting circumbinary planet (PH1) around KIC 4862625, an eclipsing binary in the Kepler field. The planet was discovered by volunteers searching the first six Quarters of publicly available Kepler data as part of the Planet Hunters citizen science project. Transits of the planet across the larger and brighter of the eclipsing stars are detectable by visual inspection every ~137 days, with seven transits identified in Quarters 1-11. The physical and orbital parameters of both the host stars and planet were obtained via a photometric-dynamical model, simultaneously fitting both the measured radial velocities and the Kepler light curve of KIC 4862625.The 6.18 $pm$ 0.17 Earth radii planet orbits outside the 20-day orbit of an eclipsing binary consisting of an F dwarf (1.734 +/- 0.044 Solar radii, 1.528 +/- 0.087 Solar masses) and M dwarf (0.378 +/0 0.023 Solar radii, 0.408 +/- 0.024 solar masses). For the planet, we find an upper mass limit of 169 Earth masses(0.531 Jupiter masses) at the 99.7& confidence level. With a radius and mass less than that of Jupiter, PH1 is well within the planetary regime. Outside the planet's orbit, at ~1000 AU, a previously unknown visual binary has been identified that is bound to the planetary system, making this the first known case of a quadruple star system with a transiting planet.

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Two suns, let alone four, would make for some very irregular tides.. or is that moons?

Suns would have an affect on tides, you'd have to work out what difference they would make depending on their mass and distance.

" The strength of the sun's gravity is 179 times that of the moon's but the moon is responsible for 56% of the earth's tidal energy while the sun claims responsibility for a mere 44% (due to the moon's proximity but the sun's much larger size)."

You could easily work it out. Using inverse cubes (which is how tidal deteriorates, as opposed to inverse squares of gravitational) you could figure how much of an effect a massive body would have on an earth-like body at any distance.

In the classic Braben game Elite 2 (which features a 3D galaxy of some 10^9 stellar systems), multi-star systems are almost as common as solitary ones, with everything from binaries to ternaries, quarternary, quintuple and sextuple systems to be found. Given the scale and procedural nature of the game, there's a good chance it contains an exact replica of this system too, i'd bet...

Last month there was a story here about a planet in a binary star system. I wondered why this would be considered so unusual, and was taken to task by another commenter who considered anyone w/o knowledge of orbital mechanics to be beneath stupid to suggest such a thing.

But Jupiter is not much smaller than is required to form a star, so what if it had formed in the orbit of Mercury instead, and ignited? Would that preclude the rest of the system forming as it did? What if it had ignited where it is, and Saturn had also been large enough to become a star?

I have a feeling that we are only on the cusp of discoveries in astronomy that will boggle the mind of even the most hubristic. I refer everyone to Clarke's first law:

"When a distinguished but elderly scientist states that something is possible, he is almost certainly right. When he states that something is impossible, he is very probably wrong."[/q}

shouldn't the reports of an Earth sized planet found around the orbit around Alpha Centari make this story utterly unimportant,

I don't think that's how news works. You can more than one story being important at once, maybe at differing levels of importance, but there's no reason to believe that the story of the planet round Alpha Centauri would render this story "utterly unimportant", seems a little harsh. Does a younger sibling render their older sibling utterly unimportant, merely because the older sibling is no longer news? Of course not. The two stories are both important for different reasons.

But Jupiter is not much smaller than is required to form a star, so what if it had formed in the orbit of Mercury instead, and ignited? Would that preclude the rest of the system forming as it did? What if it had ignited where it is, and Saturn had also been large enough to become a star?

I'm really curious how life would be on tidally locked planets. Would there be any life on the dark side of the planet, or the light side for that matter? Its a good exercise for the imagination.

Tidal locking itself wouldn't result in "definitely no", as you'd have to factor in the star type and distance. Atmosphere would be a major player in deciding its habitability, as this would help heat transfer, as would oceans that span both dark and light sides. So life could be sustained on a tidally locked planet. But I'm no astrophysicist, you'd have to ask someone qualified for statistics.

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